Free machining steel with improved hot workability



3,169,857 Patented Feb. 16, 1965 United States Patent Ofiice The present invention relates generally to free machining steels and more particularly to a free machining steel which is readily workable at a particular range of red heat temperatures with substantially no adverse eltects.

Essentially, the present invention relates to a steel containing additions of sulphur, or tellurium, or selenium, or combinations of the three, for imparting increased machinability to the steel, together with about 1.0 wt. percent manganese and about 0.01 to 0.3 wt. percent zirconium for improving the hot workability of the steel without decreasing the machinability.

Sulphur, tellurium and selenium, although imparting increased machinability to steel, also have an adverse effect thereon in that they impart a condition known as hot shortness to the steel. Steels having a hot short condition exhibit brittleness in a range of red heat temperatures, thereby causing cracking or fissures in the steel when it is rolled at these temperatures. This condition can be alleviated by adding manganese to the steel or by adjusting the rolling temperature to above or below the range in which the hot shortness is exhibited. Each of these remedies has its disadvantages. Raising the temperature increases the expense of the rolling operation, whereas lowering the temperature reduces the plasticity of the steel so that rolling becomes more diflicult.

Manganese has its drawbacks as a hot workability increasing addition to steels containing substantial additions of machinability-increasing elements such as sulphur, tellurium or selenium because the large amount of manganese necessary to alleviate the hot shortness imparted by large additions of these elements exceeds the limit at which manganese has no substantial deleterious effect on the machinability. More specifically, if the amount of manganese required to alleviate the hot shortness is greater than about 1.0 wt. percent, the machinability will be decreased, often as much as or more than the increase in machinability due to the increase in sulphur, tellurium or the like. Accordingly, the manganese content must be maintained below about 1.0 wt. percent if the machinability of the steel is not to be afiected adversely. On the other hand, a manganese content below 1.0 wt. percent may not be enough to alleviate the hot shortness imparted to the steel by the machinability-increasing addition. Accordingly, in steels containing substantial amounts of machinability-increasing additions such as sulphur, tellurium or selenium, one of the two characteristics, machinability or hot workability, has had to be sacrificed.

In the steel of the present invention all of the above drawbacks are avoided by utilizing a combination of manganese and zirconium to relieve the hot shortness. Because zirconium is expensive and because the use of large amounts of zirconium would render the cost of the steel prohibitively expensive, the zirconium is added in combination with the manganese in percentages of both that provide the best combination of improved hot workability and economy, without decreasing the machinability of the steel.

In steels containing substantial additions of machinability-increasing elements, such as sulphur, tellurium, selenium, or combinations thereof, the best combination of manganese and zirconium, from the triple standpoint of improved hot workability, economy and lack of adverse effect on machinability, is about 1.0 wt. percent manganese and about 0.01 to 0.3 wt. percent zirconium. A

steel of this composition displays superior machinability and may be readily hot worked Without adverse effects at the desirable hot rolling temperature range of about 2000" F. to 2150 F.

A typical steel prepared in accordance with the present invention has a composition within the following ranges:

Wt. percent C 0.07-0.2. P 0.01-0.1. S 0.05-0.50. Te 0.05-0.50. Se 0.05-0.50. Mn About 1.0 max. Zr 0.01-0.3.

And the balance consisting essentially of iron.

The above percentages are permissible ranges. A preferable embodiment of a steel prepared in accordance with the present invention contains about 0.07 to 0.1 wt. percent C, about 0.07 to 0.08 wt. percent P, about 0.30 to 0.50 wt. percent S, about 0.04 to 0.15 Te and/or Se and about the same Mn and Zr contents indicated above.

Sulphur and manganese are added to the molten steel by conventional methods well known to those skilled in the art. The tellurium is added preferably when the molten steel is poured from the ladle into the ingot mold, said tellurium addition being made to the center ofthe molten stream and when the ingot mold is between about Ms to about /8 full. The zirconium addition is made in the ingot mold or in the ladle, and the zirconium addition is made after the steel has been killed with a conventional deoxidizer such as aluminum.

There has thus been described a steel containing relatively large additions of machinability-increasing elements together with an addition for alleviating hot workability, the latter being added as a combination of manganese and zirconium in percentages which provide the best combination of improved hot workability, economy, and no adverse effects on machinability.

The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, as modifications will be obvious to those skilled in the art. For example, about .01-0.3 wt. percent titanium may be substituted for the zirconium or 0.01-0.3 of zirconium and titanium in combination may be used, with 1.0 wt. percent manganese.

What is claimed is:

1. A free machining, readily hot workable steel consisting essentially of:

0.07-0.2 wt. percent carbon;

0.01-0.1 Wt. percent phosphorous;

0.30-050 wt. percent sulphur;

0.04-0.15 wt. percent of a machinability increasing addition selected from the group consisting of tellurium, selenium, and combinations thereof;

about 1.0 wt. percent manganese;

0.01-0.30 wt. percent of a hot-shortness alleviating addition selected from the group consisting of zir conium, titanium, and combinations thereof;

and a balance consisting essentially of iron.

2. A free machining, readily hot workable steel consisting essentially of:

0.07-0.1 wt. percent carbon;

0.07-0.08 wt. percent phosphorous;

0.30-0.50 Wt. percent sulphur;

0.04-0.15 wt. percent of a machinability increasing 'sisting essentially of:

007-02 ,wt. percent carbon; 0.01-0.1 Wt. percent phosphorous; 0.05-0.50'Wt. percent sulphur;

0.04-0.50 wt. percent of a machinability increasing addition selected from the group consisting of tellurium, selenium, and combinations thereof;

manganese in an amount sufficient to offset at least some of the hot shortness resulting from said sulphur and from said addition and no greater than about 1.0 wt. percent;

0.01-0.30 Wt. percentof a further hot-shortness alleviattion selected from the group consisting of 0.05-0.50 Y

wt. percent sulphur, 0.04-0.50 Wt. percent tellurium, 0.04-0.50 wt. percent selenium, and combinations 7 thereof; said machinability increasing addition being present in an amount producing hot shortness greater than that which can be offset by 1.0 wt. percent manganese;

manganese in an amount suflicieht to offset at least some of said hot shortness resulting from said addition'and. no greater thanabout 1.0 wt. percent; 0.01-0.30 wt. percent of a:further hot-shortness alleviating addition selected from the group consisting of zirconium, titanium, andcombinations thereof; and a balance consistingessentially of iron.

6. In steel containing a machinability-increasing, hot

shortness-irnparting addition selected from the group consisting of 0.05-0.50 wt. percent sulphur, 0.04-0.50 wt.

percent tellurium, 0.04-0.50v wt. percent selenium and combinations thereof, with said addition being present in an amount producing hot shortness greater than that which canbe offset by 1.0 wt. percent manganese;

1 hot shortness-alleviatingadditions consisting essentially of: manganese in an amount sufficient'to oitset ,at least some of-said machinability-increasirig hot shortness resulting from said addition and no greater than about 1.0 wt. percent; I

' and 0.01-0.30 wt. percent of a further hot shortnessalleviating addition selected fro'mthe group consistting of zirconium, titanium and combinations thereof.

References Cited in the file of this-patent UNITED. STATES PATENTS 1,507,452 Becket Sept. 2, 1924 1,660,409 Becket Feb. 28, 1928 2,009,714 Palmer July 30; 1935 OTHER REFERENCES The Iron Age, December-13, 1923, Waterhouse'et al. (page 1575 reliedon).

Metal 'Progressjiuly 1942.,Mitchell (page 58 relied 

2. A FREE MACHINING, READILY HOT WORKABLE STEEL CONSISTING ESSENTIALLY OF: 0.07-0.1 WT. PERCENT CARBON; 0.07-0.08 WT. PERCENT PHOSPHOROUS; 0.30-0.50 WT PERCENT SULPHUR; 0.04-0.15 WT. PERCENT OF A MACHINABILITY INCREASING ADDITION SELECTED FROM THE GROUP CONSISTING OF TELLURIUM, SELENIUM, AND COMBINATIONS THEREOF; ABOUT 1.0 WT. PERCENT MANGANESE; 0.01-0.30 WT. PERCENT ZIRCONIUM; AND A BALANCE CONSISTING ESSENTIALLY OF IRON. 